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Hirade, Tetsuya; Furuta, Hikaru*; Torikai, Yuji*; Fujimura, Yuki; Michishio, Koji*
JJAP Conference Proceedings (Internet), 9, p.011106_1 - 011106_7, 2023/00
Positron annihilation lifetime (PAL) measurements by use of a positron source of 
Na were performed for polycrystalline ITER-grade tungsten samples exposed to low-energy deuterium plasma. The energy of deuterium plasma was low and then it was expected that it would affect just near-surface region. However, we obtained the longer mean positron annihilation lifetime in the tungsten samples exposed to the low-energy deuterium plasma than the virgin tungsten samples. Moreover, almost same longer values were obtained even on the other (no exposed) side of the samples, although the thickness of the samples were about 2 mm. Although, there has been no report of observation of defect formation by existence of hydrogen or deuterium in tungsten, the results indicated that deuterium existence in tungsten can be one of reasons of defects formation.
Al
GaO
scintillators by gamma-ray-induced positron annihilation lifetime spectroscopyFujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.
Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08
Times Cited Count：5 Percentile：32.24(Physics, Applied)To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAl
O, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg
ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*
Journal of Physics; Conference Series, 791(1), p.012029_1 - 012029_4, 2017/02
Times Cited Count：2 Percentile：62.42(Physics, Multidisciplinary)We tried to observe the positron annihilation rates near surface of (room temperature ionic liquids) IL's, such as N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) by use of the perpendicular slow positron beamline installed at AIST. The vaper pressure of TMPA-TFSI is very small and hence it is possible to measure the positron annihilation rate in vacuum chamber directly. This represents the first energy variable experimental results of the positron annihilation rate at the near surface of an IL. The triplet positronium annihilation rate seems to be larger at nearer region to the surface of the IL's.
Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Hirade, Tetsuya; Oshima, Nagayasu*
NanotechJapan Bulletin (Internet), 8(3), 5 Pages, 2015/07
Studying the creation and time evolution of defects is an important issue for interpreting the hydrogen embrittlement mechanism of steels. We have been studied the relationship between hydrogen embrittlement of high strength steel and lattice defects associated with hydrogen by thermal desorption analysis (TDA) and positron probe microanalyzer (PPMA).
/SiC interface probed by a slow positron beamMaekawa, Masaki; Kawasuso, Atsuo; Chen, Z. Q.; Yoshikawa, Masahito; Suzuki, Ryoichi*; Odaira, Toshiyuki*
Applied Surface Science, 244(1-4), p.322 - 325, 2005/05
Times Cited Count：13 Percentile：49.91(Chemistry, Physical)no abstracts in English
Maekawa, Masaki; Masuno, Shinichi*; Hirano, Takeshi*; Kondo, Masakazu*; Kawasuso, Atsuo; Ito, Hisayoshi; Okada, Sohei
JAERI-Tech 2003-039, 52 Pages, 2003/03
JAERI-Tech-2003-039.pdf:5.14MB
no abstracts in English
Maekawa, Masaki; Kawasuso, Atsuo; Okada, Sohei; Ito, Hisayoshi
Materials Science Forum, 363-365, p.658 - 660, 2001/05
no abstracts in English
Ishimoto, Kazukiyo; Hirade, Tetsuya; Suzuki, Junichi*; Okubo, Nariaki; Suzuki, Kazuhiko*
no journal, ,
Positron annihilation lifetime measurements were performed to evaluate defects introduced by plastic deformation of SUS316 specimens. Although there was almost no long lifetime component before the deformation, a component with a lifetime of 177 picosecond gave intensity of 86% after the deformation of 40%. This lifetime corresponds to the lifetime of positrons trapped in mono vacancies. As a result of small angle neutron scattering experiments, the enhancement of scattering intensity at the plastic strain greater than about 50% where necking of the specimens was initiated, probably, indicated the formation of 
m voids. The defect size observed by the positron annihilation methods and the void size observed by the small-angle scattering method were in different scale, therefore the combination of the two methods would be useful to evaluate the microstructural changes on the way to the fracture.
Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*
no journal, ,
A vertical slow positron beam was used to investigate the surface of a room temperature ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI). Measurement of positron lifetimes indicated a higher Ps formation probability and shorter ortho-Ps annihilation lifetime in near surface of TMPA-TFSI than in the bulk. These changes are probably caused by the layered structure in near surface of TMPA-TFSI. Vertical slow positron beams are a strong tool to investigate the surface of room temperature ionic liquids.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
Positron annihilation lifetime spectroscopy (PALS) is very strong tool to investigate sab-nanometer scale defects in metals and semiconductors. PALS is based on the 
-ray measurement techniques and it is difficult to measure radioactive samples such as Neutron irradiated samples. Therefore we are creating a method by which you can measure PALS for one very small radioactive sample. It is needed to reject events that positrons annihilate at outside of the sample. We placed the sample at a small space between scintillators and used signals from the scintillators for the anti-coincidence method to reject the events. We succeeded to reject 20% of the events.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
Positron lifetime measurement (PALS) is a useful tool for evaluating nanometer-sized defects in materials such as metals and semiconductors. However, PALS measurement required two flat specimens placed at both sides of the positron source therefore it was difficult to apply PALS for one complicated shaped small specimen. Purpose of this research is developing a PALS method that can be applied for one small specimen having complicated shape. We succeeded to measure PALS spectra with just one specimen.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
The positron lifetime measurement method (PALS) is a useful tool for evaluating nanometer-sized vacancy defects in metals and semiconductors. Especially in the material development for nuclear fusion reactors or nuclear reactors, elucidation of damage behavior by radiation is an important subject. However, PALS always needs to have large enough two specimens. At present, miniaturization of sample is strongly required to reduce radioactivity, but this restriction is a big hindrance to the application of PALS. In this research, we developed a measurement system that can measure positron lifetime with one specimen of arbitrary shape. Positron surrounding the specimen with a scintillator and not incident on the specimen was detected by the light emission of the scintillator, and PALS measurement in the sample was attempted by excluding treatment (anti-coincidence). As a result, we succeeded in obtaining a spectrum which is roughly in agreement with the conventional measurement method.
Oka, Toshitaka; Kino, Yasushi*; Sekine, Tsutomu*
no journal, ,
Polyethylene is widely used for an insulator and a covering material in nuclear plants. it degrades with irradiation or oxidation during long-term usage, the evaluation of the degradation is important for the safety of the facility. Electron-beam was irradiated high density polyethylene (HDPE). Chemical structure was examined by micro-FT-IR, gel fraction measurement, and electron spin resonance, nanostructure was examined by positron annihilation lifetime spectroscopy (PALS), periodically. Ortho-Positronium (o-Ps) intensity shows the linear relationship between the gel fraction, the relationship shifts toward the smaller o-Ps intensity and lower gel fraction with elapsed time, suggesting that HDPE degrade even after 3 years from the irradiation due to the long-term oxidative degradation. The obtained results shows that PALS can monitor the structural change induced by the irradiation, non-destructively.
Taira, Yoshitaka*; Fujimoto, Masaki*; Fujimori, Kosuke*; Kitaura, Mamoru*; Zen, H.*; Okano, Yasuaki*; Hosaka, Masahito*; Yamazaki, Junichiro*; Kato, Masahiro*; Hirade, Tetsuya; et al.
no journal, ,
For general positron sources, radioisotopes such as Na are often used. However, there is a problem that positrons cannot probe the deep region of metal materials with a thickness of 1 mm or more. Gamma-ray induced positron annihilation lifetime measurement (GiPALS) is a method for generating positrons in bulk samples with a thickness of several centimeters and samples placed in vessels such as high temperature and/or pressure furnaces. The annihilation lifetime of positrons is about 200 ps for metal materials, so it is important to use gamma rays with a shorter pulse width for GiPALS in order to accurately measure the positron lifetime. We have succeeded in the proof-of-principle experiment for GiPALS of ultra-short pulse gamma rays with a pulse width of 2 ps, which was originally developed using 90
collision laser Compton scattering at UVSOR.
Taira, Yoshitaka*; Fujimoto, Masaki*; Fujimori, Kosuke*; Kitaura, Mamoru*; Zen, H.*; Okano, Yasuaki*; Hosaka, Masahito*; Yamazaki, Junichiro*; Kato, Masahiro*; Hirade, Tetsuya; et al.
no journal, ,
For general positron sources, radioisotopes such as Na are often used. However, there is a problem that positrons cannot probe the deep region of metal materials with a thickness of 1 mm or more. Gamma-ray induced positron annihilation lifetime measurement (GiPALS) is a method for generating positrons in bulk samples with a thickness of several centimeters and samples placed in vessels such as high temperature and/or pressure furnaces. The annihilation lifetime of positrons is about 200 ps for metal materials, so it is important to use gamma rays with a shorter pulse width for GiPALS in order to accurately measure the positron lifetime. We have succeeded in the proof-of-principle experiment for GiPALS of ultra-short pulse gamma rays with a pulse width of 2 ps, which was originally developed using 90 collision laser Compton scattering at UVSOR.
Kitaura, Mamoru*; Fujimori, Kosuke*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Hirade, Tetsuya; Kamada, Kei*; Watanabe, Shinta*; Onishi, Akimasa*
no journal, ,
Positron annihilation spectroscopy is the only way to investigate the properties of cation vacancies because they are negatively charged. We generated high-energy pulsed gamma rays by the vertical collision of an ultrashort pulse laser and electron beam. In this study, we investigated the vacancy-type defects present in the crystals of GAGG(GdAlGaO), GAGG: Ce and GAGG: Ce, Mg by positron annihilation lifetime spectroscopy using the high-energy gamma rays. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
AlGaO crystals revealed by gamma-ray induced positron annihilation lifetime spectroscopyFujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Hirade, Tetsuya; Kamada, Kei*; Watanabe, Shinta*; Onishi, Akimasa*
no journal, ,
We generated high-energy pulsed gamma rays by the vertical collision of an ultrashort pulse laser and electron beam. In this study, we investigated the vacancy-type defects present in the crystals of GAGG(GdAlGaO), GAGG: Ce and GAGG: Ce, Mg by positron annihilation lifetime spectroscopy using the high-energy gamma rays. The lifetime of the defect-related component was significantly changed by Mg co-doping. This indicates that the Al/Ga vacancies disappear. This fact corresponds well with the suppression of the phosphorescence component and is an important result showing that the Mg co-doping is effective in suppressing the shallow electron capture center.
Hirade, Tetsuya
no journal, ,
Most of the positron annihilation lifetime measurements by simultaneous measurement of - using Na-22 as a positron source are performed only with a digital oscilloscope without using any analogue module. Although, it is known that the time resolution is improved by the double-stop measurement that measures both annihilation gamma rays, a method of operating by creating a trigger signal for a digital oscilloscope with an analog module has been introduced, and it is not as widespread as the usual single-stop method. Therefore, I tried a double-stop measurement method using the advanced trigger function provided in the digital oscilloscope that does not use an analogue module and confirmed that the measurement was possible.
Yabuuchi, Atsushi*; Awaji, Ryo*; Hirade, Tetsuya; Fujinami, Masanori*; Oshima, Nagayasu*; Takai, Kenichi*; Taira, Yoshitaka*
no journal, ,
In situ measurements of positron annihilation lifetimes have been performed at the UVSOR synchrotron radiation facility to evaluate defects formed during tensile deformation in pure iron using the gamma-ray induced positron annihilation spectroscopy technique. A 66 MeV gamma-ray pulse beam with a diameter of 3 mm was irradiated to the centre of the sample while stretching it to a nominal strain of 7 or more at a strain rate of 2.2
10
/s. The positron lifetime change during the tensile deformation of iron specimens was observed. Positron lifetime measurements have often been performed after the deformation of the sample. Unlike these results, it was found that the lifetime change at the initial deformation stage was very small in these In situ measurements.
Doshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
It has been reported that oxygen vacancies in cerium oxide (CeO) affect catalytic activity. There is a need for highly sensitive in-situ measurements of the state and concentration of oxygen vacancies during catalytic reactions, and we are considering using the positron annihilation method. This time, we measured samples with different particle sizes to clarify the sites where positrons are trapped. From the lifetime spectrum of a particle size of 2 nm, which has a high intensity of the long-lived component, we first determined the lifetime value of the longest-lived component to be 390.8
1.6 ps. Next, in the lifetime spectrum of a particle size of 60 nm, where the longest lifetime component is the smallest, the longest lifetime component was fixed at 390.8 ps, and the lifetime value of the other positron trap site was determined to be 199.47.4 ps. These values are close to the lifetimes of positrons trapped in surface and neutral oxygen defects in first-principles calculations.
